Sinnott and Bartletl — Coniferous Woods. 287 



Paracupressinoxylon potomacense n. sp. 



Annual rings poorly marked. Wood parenchyma abundant. 

 Tracheids exceedingly narrow, their radial walls provided with 

 a single row of small bordered pits. " Bars of Sanio " absent. 

 Pits from tracheid to ray generally one to the narrow crossing 

 field ; if two, then one above the other. Pore narrow to rather 

 wide, oblique. Rays thin-walled, pitless, very shallow, usually 

 from one to three cells in height. Traumatic resin canals well 

 developed. 



Localities : Central High School and Meridian Hill Park, 

 Washington, D. C. 



Horizon : Patuxent. (Lower Cretaceous.) 



Structure. 



Paracupressinoxylon potomacense is represented in our col- 

 lection only by lignite and was found most abundantly at the 

 Meridian Hill Park locality. Its tracheids are very much 

 smaller, averaging 100-120 to the millimeter in the transverse 

 section, or only about a third as wide as those of Podocarp- 

 oxylon McGeei. Annual rings are very poorly marked. Wood 

 parenchyma, very thin-walled, is abundant and scattered 

 throughout the year's growth. Its cells are almost invariably 

 filled with a resinous or mucilaginous substance. The pits on 

 the radial walls of the tracheids are necessarily small and never 

 occur in more than one row. They are numerous, especially 

 towards the ends of the tracheids, but are very rarely flattened 

 by mutual contact. Even in the best preserved material, 

 " bars of Sanio " seem to be completely absent. The ray cells, 

 like the wood parenchyma; are thin-walled and pitless. There 

 are either one or two pits on the small crossing field between 

 ray cell and tracheid, but these pits are generally large in pro- 

 portion to the field. The pores are elongated obliquely or in 

 some cases almost horizontally and are sometimes rather large. 

 Most of the rays are very shallow, running from one to three 

 cells in height, although a few are taller. We were fortunate 

 enough to secure two specimens which, though not particu- 

 larly well preserved, show indubitably the presence of healed 

 wounds. Running back from the edges of the wound cap on 

 either side is a tangential row of traumatic resin canals. Most 

 of these have suffered from lateral compression, but that they 

 are true resin canals is made clear by the radial section, which 

 shows well-developed epithelial cells and tyloses.* In the 



* Jeffrey lias described and figured the occurrence of traumatic resin 

 canals in an unnamed coniferous wood from the Potomac formation at 

 Dutch Gap, Va., which is perhaps identical with ours, although the other 

 characters are unknown. (Jeffrey, E. C, Wound Eeactions of Brachvphyl- 

 lum, Ann. Bot,, xx, 383-894, 1906.) 



